@article{GT_2011_15_2_a0,
     author = {Schommer-Pries, Christopher~J},
     title = {Central extensions of smooth 2{\textendash}groups and a finite-dimensional string 2{\textendash}group},
     journal = {Geometry & topology},
     pages = {609--676},
     publisher = {mathdoc},
     volume = {15},
     number = {2},
     year = {2011},
     doi = {10.2140/gt.2011.15.609},
     url = {http://geodesic.mathdoc.fr/articles/10.2140/gt.2011.15.609/}
}